They're SO extra!
Extras are additional attributes that may have both Permissions and Costs. Often, an Advantage or Disadvantage might be good fodder for an Aspect or Trouble, respectively. If, for instance you wanted to have The Fastest Ride on the East Coast, that's a fine Aspect. It establishes facts about your character and it's double-edged. Yes, you can sure get there quick or get away quick as needs be, but if you know for sure it's the fastest, you have definitely tested this and probably your vehicle, if not yourself, has a reputation just as negative with law enforcement as it is positive with gearheads.
But maybe you have a lot of aspects already, as in you have all of them filled in and want to keep them. Or, conversely, maybe your reliable vehicle, steady income, or place to crash isn't important enough to who your character actually is to take up an aspect slot but may be important enough a distinction in your chronicle that it needs mentioning (and maybe purchasing). An example might be a secure lair in a vampire campaign, a Hall of Dogooders in which to meet in a superhero story, or just a steady income.
That's where extras shine. In some RPG systems, these sorts of things might be referred to as "backgrounds" and usually have a spot on a character sheet—sometimes relegated to page two or beyond.
Extras come in two flavors: Advantages and Disadvantages. Which one has benefits and which one causes complications should be pretty obvious. Remember, these are not a replacement for any other part of your character but are instead a further refinement. They also allow characters to pool their points in order to create a significant advantage with a shared cost, like the aforementioned Hall.